1. Field of the Invention
The present invention relates to an improvement in an image forming apparatus, such as a laser printer or an electronic copying machine, for forming an image in accordance with image data transmitted from, e.g., a host unit.
2. Description of the Related Art
A conventional image forming apparatus, such as a laser printer, an electronic copying machine, or the like is typically connected to a host unit, such as a computer, an image reader unit, or the like. This apparatus forms an image on an image forming medium, e.g., a sheet of paper in accordance with image data transmitted from this host unit.
In such an image forming apparatus, a strong demand has arisen for an improvement in operation of the apparatus by reducing labor improvement for paper replenishment, increasing speed of image formation, improving edit functions, etc. In conventional image forming apparatuses, however, many problems currently exist. For example, the maximum printable width of paper (although envelopes, gummed labels, and the like are used as an image forming medium in addition to paper, all theseforms will hereinafter by referred to as paper) is limited by the width of the photosensitive drum in the apparatus. Therefore, sheets of paper having a plurality of sizes which are limited by the maximum width of the drum are respectively set in corresponding paper feed cassettes, and paper of a predetermined size is selected in accordance with an application purpose. In this case, the size of a paper cassette is set to allow paper of the maximum size to be stored therein. Paper of a smaller size is set in this cassette by positioning a corner of the paper at an arbitrary origin of the cassette.
In setting of paper, paper of the same size is set by aligning a long side of the paper with the paper feed direction, or by aligning a short side of the paper with the paper feed direction. When the paper which is set in this manner is to be printed, portrait or landscape printing is performed. In portrait printing, printing is performed on a line extending in a direction perpendicular to the paper feed direction. In landscape printing, printing is performed on a line extending parallel to the paper feed direction. Designation of a direction of printing on paper, which includes both the printing schemes described above, is called orientation.
Data to be printed on paper may be lost depending on a manner of setting paper and a designation of orientation. For example, assume that paper is set by aligning its short side with the paper feed direction and that landscape printing is carelessly designated by an operator in spite of the fact that portrait printing should be designated. In such a case, the operator must reset the paper by aligning its long side with the paper feed direction and must resume the printing operation. If this occurs, paper will be wasted, and moreover a cumbersome and time consuming operation is required to resume printing, resulting in a less effective operation.
Some conventional image forming apparatuses employ two paper feed cassettes to store paper of the same size. In one cassette, paper is set by the manner of aligning its long side with the paper feed direction. In the other cassette, paper is set by the manner of aligning its short side with the paper feed direction. However, when a particular paper feed cassette is selected having a desired paper feed direction, and the paper feed cassette becomes empty during printing, the printing operation is stopped while a display on the apparatus signifies that the cassette is empty. Therefore, the maximum number of sheets of paper on which images can be continuously formed is limited by the capacity of one paper feed cassette. If a large quantity of image forming is required, paper replenishment must be frequently performed, thereby resulting in lower efficiency.
The manner of aligning a short side of paper with the paper feed direction allows a larger number of images to be formed on paper per unit time compared to the other manner of paper setting. This is because the number of sheets of paper to be fed per unit time can be increased when the paper is set by aligning a short side of paper with the paper feed direction where the paper feed speed is constant.
In such a conventional apparatus, however, once an operator sets paper by aligning its long side with the paper feed direction, the paper feed operation cannot be switched to feeding sheets of paper set with their short sides aligned with the paper feed direction without stopping the paper feed operation. As a result, it often takes a long time to form images, thus making a high-speed printing operation impossible.
Further, such conventional image forming apparatuses are quite expensive. In addition, if the apparatus is connected only to a single host unit, its operation efficiency becomes undesirably low because of the limited access. For this reason, a multiport arrangement for allowing access of a plurality of host units is widely employed. Image forming apparatuses, which employ such a multiport arrangement accessed by a plurality of host units, are designed to form images of various sizes. Therefore, these apparatuses generally have paper feed cassettes which store sheets of paper of various sizes in order to allow formation of the images of various sizes described above.
In order to respond to image forming requests from these host units, the image forming apparatus receives data associated with the size of paper, i.e., data for designating a form length, as a command from a given host unit prior to reception of image data, and analyzes the command to check whether paper is present in a corresponding paper feed cassette. If no paper is present, a signal is generated that the cassette is empty to alert the operator to replenish the paper.
If the operator is present near the image forming apparatus, this will present no problem. However, if the operator is not present near the apparatus, i.e., an unmanned operation is performed, paper replenishment is not performed. This may create a number of problems. For example, a receiving buffer, which is arranged in the image forming apparatus to store temporarily image data, is filled with data, and hence either cannot respond to an image forming request with respect to paper of another size from another host unit or else it will lose received image data. Further, if a given host unit is requested to stop transmitting image data, processing on the host unit side will be delayed.
When a plurality of sets of sheets are to be printed by the above-described image forming apparatus, a designated number of sheets are first printed with respect to one-page image data supplied from a host unit, and a designated number of sheets are then printed with respect to the next one-page image data. Similarly, a designated number of sheets are printed for each page. The printed sheets, which are obtained by printing the designated numbers of sheets for all the pages in this manner, are not sorted. Therefore, the operator must sort the printed sheets in the order of pages in units of sets upon completion of printing of all the sheets, resulting in reduce efficiency.